System and method for engine exhaust injection before and after catalytic converter

Abstract

Engine systems and methods use a dual air injection method to control exhaust reactions and maintain temperatures below maximum limits of exhaust system components during engine rich operating conditions. Dual air injectors are provided in the exhaust system, one upstream of the catalytic converter and one downstream of the catalytic converter. Providing air injection before and / or after the converter helps to convert all HC, CO, and PM emissions while keeping the catalyst temperature below catalyst protection temperature limits. The amount of air injection can be controlled and diagnosed by monitoring the temperatures before and after the catalytic converter. To reduce cost, the catalytic converter can be a three-way catalytic converter, or a downstream dual- way catalytic converter can be added if further emission reduction is required.

Description

Technical Field

[0001] This disclosure relates to engine systems and methods and exhaust systems thereof, and more specifically to engine systems and methods that employ air injection into the exhaust system before and / or after the catalytic converter system to reduce hydrocarbon (HC), carbon monoxide (CO) and / or particulate matter (PM) emissions and improve the robustness of the exhaust system. Background Technology

[0002] Internal combustion engines convert fuel and air into various compounds while extracting energy to perform intended functions, such as propelling vehicles. The compounds produced in the engine can also be converted or treated by various after-treatment systems. Dual-way catalytic converters convert HC and CO, as well as oxides, into harmless elements or compounds. Three-way catalytic converters are designed for converting HC, CO, and nitrogen oxides.

[0003] Vehicle engines typically operate under stoichiometric conditions. However, in certain situations, to achieve specific performance properties, operation may deviate from stoichiometry. In such non-stoichiometric conditions, aftertreatment systems may not operate optimally. The characteristics of exhaust gas leaving the engine are influenced by numerous variables, making optimal aftertreatment challenging. These challenges are compounded by limitations imposed by aftertreatment systems, such as catalyst temperature limitations.

[0004] Therefore, it is desirable to provide an engine system with an exhaust aftertreatment system that can provide optimal conversion and component protection while limiting undesirable emissions or emissions exceeding regulatory requirements. Furthermore, other desirable features and characteristics of this disclosure will become apparent from the following detailed description and appended claims, taken in conjunction with the accompanying drawings and the foregoing technical and background information. Summary of the Invention

[0005] Engine systems and methods, with optional combinations, employ air injection before and / or after the catalyst in the exhaust system to optimally convert HC, CO, and / or PM into harmless components, including under high exhaust mass flow conditions, while keeping exhaust system components below maximum temperature limits. In various embodiments, the engine consumes fuel and air to produce an exhaust stream. The exhaust system directs the exhaust stream from the engine to the tailpipe for emission. A catalytic converter is included in the exhaust system and configured with upstream and downstream air injection.

[0006] In another embodiment, the mixer is disposed in the exhaust system downstream of the catalytic converter. The mixer defines an oxidation chamber. A mixing plate is disposed in the oxidation chamber and configured to allow exhaust flow through the oxidation chamber.

[0007] In another embodiment, a first temperature sensor is disposed in the exhaust system upstream of the catalytic converter, and a second temperature sensor is disposed in the exhaust system downstream of the catalytic converter. The controller is configured to control the flow rate through the upstream air injector based on the first temperature sensor. The controller is configured to diagnose the conversion performance of the catalytic converter by calculating the released heat of conversion based on the second temperature sensor.

[0008] In another embodiment, the upstream air injector includes a first orifice having a first flow area, and the downstream air injector includes a second orifice having a second flow area. The controller is configured to control the flow rate through the air injectors, including injecting air through at least one of the air injectors, to keep the catalytic converter below its maximum temperature limit, wherein the first flow area is smaller than the second flow area, to improve the mixing and precision of the flow rate through the upstream air injector and optimize the exhaust temperature reduction caused by the flow rate through the downstream air injector.

[0009] In another embodiment, the flow rate is controlled by an air injector such that when the temperature of the exhaust stream upstream of the catalytic converter is below a threshold temperature, air is injected into the exhaust stream only through the upstream air injector and not through the downstream air injector.

[0010] In another embodiment, the flow rate is controlled by an air injector such that when the temperature of the exhaust stream upstream of the catalytic converter is higher than a threshold temperature, air is injected into the exhaust stream only through the downstream air injector and not through the upstream air injector.

[0011] In another embodiment, the air flow is controlled by air injectors to: achieve air injection when the engine equivalence ratio is greater than one; when the temperature of the exhaust flow upstream of the catalytic converter is lower than a first threshold temperature, air is injected into the exhaust flow only through the upstream air injector; when the temperature of the exhaust flow upstream of the catalytic converter is higher than a second threshold temperature, air is injected into the exhaust flow only through the downstream air injector; and when the temperature of the exhaust flow upstream of the catalytic converter is between the first threshold temperature and the second threshold temperature, air is injected into the exhaust flow through both the upstream and downstream air injectors.

[0012] In another embodiment, the controller is configured to control air injection through the upstream and downstream air injectors based on the equivalence ratio of the engine during operation. The equivalence ratio represents the fuel-air ratio of the engine during operation compared to the engine's stoichiometric ratio. When the catalytic converter includes a dual-effect catalytic converter and the equivalence ratio is greater than one, the controller is configured to control the temperature in the catalytic converter to achieve a complete carbon monoxide and hydrocarbon reaction. When greater emission reductions are required, the catalytic converter can be a pair of bottom-plate catalytic converters, such as a three-way catalytic converter, followed by a dual-effect catalytic converter, or, for cost reduction, the catalytic converter can be a single dual-effect or three-way catalytic converter.

[0013] In another embodiment, the controller is configured to control the flow rate through the air injectors such that when the engine operating speed is below a threshold speed, air is injected into the exhaust stream only through the upstream air injectors and not through the downstream air injectors.

[0014] In another embodiment, the controller is configured to control the flow rate through the air injectors to inject air into the exhaust stream only through the upstream air injectors when: the equivalence ratio of the engine is greater than 1.0 during operation; the temperature of the exhaust stream upstream of the catalytic converter is lower than a threshold temperature; and the engine is operating at a speed lower than a threshold speed.

[0015] In several other embodiments, the method includes configuring an engine system for consuming fuel and air to generate an exhaust stream. The exhaust stream is directed from the engine to a tailpipe via an exhaust system for emission. A catalytic converter is disposed in the exhaust system. A first air injector is disposed in the exhaust system upstream of the catalytic converter, and air is injected into the exhaust system upstream of the catalytic converter for a first set of engine operating conditions. A second air injector is disposed in the exhaust system downstream of the catalytic converter, and air is injected into the exhaust system downstream of the catalytic converter for a second set of engine operating conditions.

[0016] In another embodiment, the mixer is disposed in the exhaust system downstream of the catalytic converter. The mixer defines an oxidation chamber, and a mixing plate is disposed within the oxidation chamber such that exhaust gas flow is allowed to pass through the mixing plate into the oxidation chamber.

[0017] In another embodiment, the injection system is coupled to a first air injector and a second air injector. A first branch pipe section leads to the first air injector, and a second branch pipe section leads to the second air injector. A first mass flow controller controls the flow rate through the first air injector, and a second mass flow controller controls the flow rate through the second air injector.

[0018] In another embodiment, the method includes controlling the flow rate through an air injector and injecting air through at least one of the air injectors to keep the catalytic converter below a maximum temperature limit while increasing the temperature of the exhaust stream downstream of the catalytic converter.

[0019] In another embodiment, the method includes controlling the flow rate through the air injector, and injecting air into the exhaust stream only through the upstream air injector when the temperature of the exhaust stream upstream of the catalytic converter is below a threshold temperature.

[0020] In another embodiment, the method includes controlling the flow rate through the air injector, and injecting air into the exhaust stream only through the downstream air injector when the temperature of the exhaust stream upstream of the catalytic converter is higher than a threshold temperature.

[0021] In another embodiment, the method includes controlling the flow rate through the air injectors to achieve air injection when the engine's equivalence ratio is greater than one. When the temperature of the exhaust stream upstream of the catalytic converter is below a first threshold temperature, air is injected into the exhaust stream only through the first air injector. When the temperature of the exhaust stream upstream of the catalytic converter is above a second threshold temperature, air is injected into the exhaust stream only through the second air injector. When the temperature of the exhaust stream upstream of the catalytic converter is between the first and second threshold temperatures, air is injected into the exhaust stream through both the upstream and downstream air injectors.

[0022] In another embodiment, the method includes controlling air injection through upstream and downstream air injectors during operation based on the engine's stoichiometric ratio. The stoichiometric ratio represents the engine's fuel-air ratio during operation compared to the engine's stoichiometric ratio.

[0023] In another embodiment, the method includes controlling the flow rate through the air injectors to achieve air injection into the exhaust stream only through the upstream air injectors when: the equivalence ratio of engine operation is greater than 1.0, the temperature of the exhaust stream upstream of the catalytic converter is below a threshold temperature, and the engine operation speed is below a threshold speed.

[0024] In several other embodiments, the engine system includes an engine configured to consume fuel and air to generate an exhaust stream. An exhaust system is configured to direct the exhaust stream from the engine to a tailpipe for emission and includes a catalytic converter within the exhaust system. One air injector is disposed in the exhaust system upstream of the catalytic converter and configured to inject air into the exhaust system upstream of the catalytic converter. Another air injector is disposed in the exhaust system downstream of the catalytic converter and configured to inject air into the exhaust system downstream of the catalytic converter. An exhaust temperature sensor is disposed in the exhaust stream upstream of the catalytic converter, and another exhaust temperature sensor is disposed in the exhaust stream downstream of the catalytic converter. Based on inputs of a first exhaust temperature from a first exhaust temperature sensor and a second exhaust temperature from a second exhaust temperature sensor, a controller is configured to implement air injection: when the first exhaust temperature is below a first threshold temperature, only the upstream air injector is used; when the first exhaust temperature is above a second threshold temperature, only the downstream air injector is used; and when the second exhaust temperature is at the maximum temperature limit of the catalytic converter, both the first and second air injectors are used. Attached Figure Description

[0025] Exemplary embodiments will be described below in conjunction with the following figures, wherein the same numerals denote the same elements, and wherein:

[0026] Figure 1 This is a schematic diagram of an engine system with an exhaust system according to various embodiments, the exhaust system having pre-catalyst air injection and post-catalyst air injection and optional mixing features;

[0027] Figure 2 According to various embodiments Figure 1 A schematic diagram of the air injection system of the engine system;

[0028] Figure 3 The illustrations are based on various embodiments. Figure 2 Data flow diagram of the control aspects of the air injection system;

[0029] Figure 4 It is according to various embodiments for implementing control Figure 1 A flowchart illustrating the processes of the pre-catalyst air injection and post-catalyst air injection systems in the exhaust system of an engine system; and

[0030] Figure 5 It is based on various embodiments and has Figure 4 A flowchart detailing part of the process. Detailed Implementation

[0031] The following detailed description is exemplary in nature only and is not intended to limit application and use. Furthermore, it is not intended to be bound by any express or implied theory set forth in the foregoing technical fields, background art, summary of the invention, or the following detailed description. As used herein, the term "module" refers to any hardware, software, firmware, electronic control components, processing logic, and / or processor device, individually or in any combination, including but not limited to: application-specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated, or grouped) and memories executing one or more software or firmware programs, combinational logic circuits, and / or other suitable components providing the described functionality.

[0032] In this document, embodiments of the present disclosure may be described in terms of functional and / or logical block components and various processing steps. It should be understood that such block components may be implemented by any number of hardware, software, and / or firmware components configured to perform specified functions. For example, embodiments of the present disclosure may employ various integrated circuit components, such as memory elements, digital signal processing elements, logic elements, or lookup tables, capable of performing various functions under the control of one or more microprocessors or other control devices. Furthermore, those skilled in the art will understand that embodiments of the present disclosure can be practiced in conjunction with any number of steering systems, and the vehicle system described herein is merely one example embodiment of the present disclosure.

[0033] For the sake of brevity, conventional techniques related to signal processing, data transmission, signaling, control, and other functional aspects of the system (and its various operating components) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures included herein are intended to illustrate exemplary functional relationships and / or physical couplings between various elements. It should be noted that many alternative or additional functional relationships or physical connections may exist in the embodiments of this disclosure.

[0034] As disclosed herein, air injection before and / or after the catalytic converter reduces exhaust gases, such as hydrocarbons and carbon monoxide, included under enrichment conditions. At exhaust temperatures above 500°C, hydrocarbons and carbon monoxide can be converted in the exhaust pipe section in addition to those converted in the catalyst via the introduction of air into the exhaust flow. In some embodiments, this conversion can be assisted by a mixing device that creates exhaust flow conditions to increase the mixing and reaction of air and exhaust gases. Under high exhaust mass flow and high CO conditions, when the exhaust temperature downstream of the catalytic converter is naturally too low for conversion to occur in the downstream section, air injection can be used to supply sufficient oxygen upstream to raise the temperature in the catalytic converter through an exothermic reaction induced by the upstream air injection, thereby causing post-oxidation.

[0035] refer to Figure 1Engine system 20 includes an internal combustion engine 22, which in this embodiment is an eight-cylinder gasoline and air-consumption engine. Engine 22 may be naturally aspirated as shown, or in other embodiments may include a turbocharger or supercharger to pump air into the engine for combustion purposes. Engine system 20 includes an exhaust system 24 for delivering exhaust gas from the combustion chamber of engine 22 to tailpipe section 26 for emission into the atmosphere. A pair of pipe sections 28, 30 extend from engine 22 in a dual arrangement, such as extending from its exhaust manifolds 32, 34 respectively, and each pipe section extends to an aftertreatment device in the form of tightly coupled catalytic converters 36, 38. The tightly coupled catalytic converters 36, 38 may be of the three-way type to convert CO, HC, and PM at lower engine operating temperatures, such as immediately after engine start-up, due to their proximity to exhaust manifolds 32, 34. An additional catalytic converter 40 is located downstream of the base plate and performs most of the conversion during normal engine operation. Catalytic converter 40 may be of the two-way or three-way type. When the catalytic converter 40 is configured as a dual-effect type, it converts two components (including CO and HC) in the exhaust stream into other components. When the catalytic converter 40 is configured as a triple-effect type, it converts three components in the gas stream into other elements or compounds, including converting CO, HC, and nitrogen oxides into harmless elements or compounds. The catalytic converter 40 may contain a catalyst, such as platinum, palladium, or other materials. The catalyst has a maximum temperature limit to maintain its effectiveness.

[0036] In the current embodiment, a tightly coupled catalytic converter 36 is disposed after pipe segment 28, wherein a downstream pipe segment 42 extends from the tightly coupled catalytic converter 36 to connector 44. A tightly coupled catalytic converter 38 is disposed after pipe segment 30, wherein a downstream pipe segment 46 extends from the tightly coupled catalytic converter 38 to connector 44. The tightly coupled catalytic converter 36 includes a front element 48 and a rear element 50, and the tightly coupled catalytic converter 38 includes a front element 52 and a rear element 54. From exhaust manifolds 32, 34 to connector 44, exhaust system 24 is a dual exhaust system, and from connector 44 to tailpipe segment 26, exhaust system 24 is a single exhaust system.

[0037] Downstream of connector 44, exhaust system 24 includes pipe segment 45 leading from connected pipe segments 42, 46 to catalytic converter 40, followed by pipe segment 47 leading to optional mixer 56, and then tailpipe segment 26. Mixer 56 is omitted in some embodiments and is included when additional mixing / reaction of injected air and exhaust is required. Mixer 56 includes a canister 58 providing oxidation chamber 60 and includes a mixing plate 62. Mixing plate 62 is curved and includes orifices and / or gaps in oxidation chamber 60 to allow exhaust flow through oxidation chamber 60. Mixing plate 62 is disposed in oxidation chamber 60 and spans the flow path defined by canister 58 to maximize the interaction and mixing of injected air and exhaust flow. Mixer 56, with an enlarged oxidation chamber 60 located downstream of catalytic converter 40, facilitates the conversion of HC, CO, and / or PM, including under conditions of high exhaust mass flow and enriched operation of engine 22. Under some conditions, conversion is optimized by injecting air only before the catalytic converter 40 via air injector 132. Under some conditions, conversion is optimized by injecting air only after the catalytic converter 40 via air injector 134, thereby supplying fresh air to the mixer 56. Under some conditions, conversion is optimized by injecting air before the catalytic converter 40 via air injector 132 and after the catalytic converter via air injector 134.

[0038] Engine system 20 includes an intake system 70 with an air inlet 72, an air filter 74, and an intake manifold 76. The intake manifold 76 supplies air to cylinders 81-88 of engine 22 under the control of intake valves (not shown). Exhaust system 24 delivers post-combustion gases from cylinders 81-88 to the atmosphere via tailpipe section 26 under the control of exhaust valves (not shown). In intake system 70, a mass airflow sensor 90, an intake throttle valve 92, and an intake manifold pressure sensor 94 are sequentially arranged downstream of air filter 74 and upstream of intake manifold. Engine 22 is liquid-cooled and includes a coolant temperature sensor 96 to provide data on engine operating temperature. Engine system 20 is spark-ignition operated and therefore includes an ignition system 118 with individual spark plugs in each cylinder 81-88.

[0039] Engine system 20 includes a fuel system 100 for supplying fuel to cylinders 81-88. In the current embodiment, the engine is a gasoline direct injection (GDI) engine having fuel rails 102, 104 supplying fuel from fuel supply 105 to injectors 106-113. Engine system 20 also includes a control system 120, which typically includes a controller 122 coupled to various actuators and sensors. Controller 122 can receive various signals from sensors and send control signals to various actuators for the operation of engine system 20 and its associated systems. Sensors are devices for sensing observable conditions of engine system 20, and in the current embodiment include oxygen sensors 124-127 that measure the oxygen content of exhaust gas leaving engine 22 and determine the amount of residual CO directed to catalytic converter 40 after close coupling to catalytic converters 36, 38. Oxygen sensors 124-127 may be exhaust / oxygen / wide-range air-fuel (WRAF) sensors. The signals from oxygen sensors 124-127 vary according to the changing oxygen level in the exhaust and can identify unburned oxygen in the exhaust representing the CO content. Signals from oxygen sensors 124 and 126 can also be used to determine the fuel / air ratio for engine 22 operation, from which the current fuel-air equivalence ratio (EQR) can be calculated.

[0040] The sensors of engine system 20 include other typical engine system sensors, such as sensors 90, 94, 96, and additional sensors as described below. Oxygen sensors 124 and 126 measure parameters used to determine engine output emissions and, in particular, can be used to measure / determine the CO content in the airflow leaving engine 22. In the current embodiment, actuators may include intake throttle valve 92 and other typical engine system actuators and additional actuators as described below.

[0041] In the depicted embodiment, controller 122 includes processor 128 and memory device 129, and is coupled to memory device 131. Processor 128 performs the computational and control functions of controller 122 and may include any type of processor or multiple processors, a single integrated circuit such as a microprocessor, or any suitable number of integrated circuit devices and / or circuit boards that work together to perform the functions of a processing unit. During operation, processor 128 executes one or more programs and can use data, each of which can be accessed from memory device 131, and therefore, processor 128 controls the general operation of controller 122 during the execution of the processes described herein, such as those described below. Figure 4 and Figure 5 The process is described further.

[0042] Memory device 129 can be any suitable type of memory. Memory device 129 can store the above-described program and one or more stored data values, such as for short-term data access. Storage device 131 stores data, such as for long-term data access, for automatic control of engine system 20 and its associated systems, including exhaust system 24 and air injection system 130. Storage device 131 can be any suitable type of storage device. In one exemplary embodiment, storage device 131 includes a source from which memory device 129 receives a program that performs one or more embodiments of one or more processes of this disclosure, such as those described below. Figure 4 and Figure 5 The steps of the process (and any related processes) are described further. In another exemplary embodiment, the program may be directly stored in the memory device 129 and / or otherwise accessed therefrom.

[0043] The program represents executable instructions used by the electronic controller 122 and may include one or more separate programs, each comprising an ordered list of executable instructions for implementing logical functions. When executed by the processor 128, the instructions support receiving and processing signals such as those from various sensors, as well as performing logic, calculations, methods, and / or algorithms for the automatic control of the components and systems described herein. The processor 128 may generate control signals for the air injection system 130 based on logic, calculations, methods, and / or algorithms, and automatically control various components and systems of the engine system 20 and the exhaust system 24. Although the components of the control system 120 are depicted as part of the same system, it will be understood that in some embodiments, these features may include multiple systems and may employ any number of separate controllers.

[0044] Controller 122 controls the amount of fuel delivered to each cylinder 81-88 via fuel system 100. The fuel-air ratio is the ratio of the mass of fuel delivered to engine 22 to the mass of air delivered to engine 22. Given the current operating state of engine 22, the controlled amount of fuel is typically related to the amount required for stoichiometric operating conditions. Stoichiometric operation supplies the precise amount of air required for the complete combustion of the fuel delivered to cylinders 81-88, converting all delivered fuel into carbon dioxide and water. Therefore, the fuel-air ratio that provides the correct amount of air for complete combustion of the delivered fuel is called the stoichiometric ratio. EQR is the actual fuel-air ratio used under the current operating conditions of engine 22 compared to the expected stoichiometric fuel-air ratio under current conditions. Referring to fuel-air EQR means that a ratio greater than 1.0 indicates the presence of more fuel in the fuel-air mixture than is required for complete combustion (stoichiometry), while a ratio less than 1.0 indicates a fuel / excess air deficiency in the mixture. Therefore, an EQR greater than 1.0 indicates stoichiometric enrichment conditions (enrichment conditions).

[0045] Under certain operating conditions, controller 122 may deviate from stoichiometric operating conditions based on a pre-programmed algorithm of control system 120. For example, under heavy load conditions, excess fuel may be delivered to cylinders 81-88 for diagnostic and component protection purposes. When excess fuel is delivered, catalytic converter 40 may become saturated, meaning that within applicable temperature limits, complete conversion of the target components in the exhaust stream will not occur within catalytic converter 40. For example, not all HC, CO, and / or PM can be converted as desired. Therefore, additional air injection measures are described herein to address HC, CO, and / or PM remaining in the exhaust stream under non-stoichiometric and / or other conditions.

[0046] Engine system 20 includes a dual air injection system 130 in exhaust system 24, comprising air injectors 132 and 134, each configured to inject air into the exhaust stream. In this embodiment, air is drawn from intake system 70 downstream of air filter 74 by air pump 136. Air is selectively injected via air injectors 132 and / or air injectors 134 as needed by the current operating conditions of exhaust system 24 and as further described below. Air injector 132 is located adjacent to, downstream of, the tightly coupled catalytic converter 38. Being adjacent downstream means that air injector 132 is positioned to maximize its distance from catalytic converter 40 within pipe section 46. In other words, air injector 132 is positioned as close as possible to the tightly coupled catalytic converter 38 as practically possible. It should be noted that there is no air injector in pipe segment 42 downstream of the tightly coupled catalytic converter 36, because one air injection point upstream of the catalytic converter 40 is sufficient for a dual exhaust manifold arrangement, since pipe segments 42 and 46 are joined together at connector 44 before the catalytic converter 40. As used herein, upstream and downstream refer to the relative positions of something in the air / gas flow through engine system 20 from air inlet 72 to tailpipe 26. For example, air inlet 72 is upstream of air filter 74, and catalytic converter 40 is downstream of connector 44.

[0047] The dual air injection system 130 includes a pipe section 140 coupling an air pump 136 to the intake system 70 and a pipe section 142 coupling the pump to air injectors 132, 134. A branch pipe section 144 couples pipe section 142 to the air injector 132 and includes a check valve 146 to prevent backflow through the air injector 132 from the exhaust system 24. Another branch pipe section 145 couples pipe section 142 to the air injector 134 and includes a check valve 148 to prevent backflow through the air injector 134 from the exhaust system 24. It should be noted that the check valves 146, 148 can be passive or active devices and can be part of the actuator of the engine system 20. Additionally, the air injectors 132, 134 are controlled devices configured to inject a defined amount of air (as described further below) and are therefore part of the actuator of the engine system 20. Air injectors 132 and 134 may be nozzle-type air injectors with separate mass flow control valves (described below) to precisely control the delivered flow rate. In some embodiments, air injectors 132 and 134 may themselves be actuated variable orifice devices (such as air injection control valves) to precisely control the amount of air injected. In embodiments, a relatively small orifice may be included in air injector 132 to improve air injection accuracy and mixing, and (relative to air injector 132), a larger nozzle orifice may be included in air injector 134 to reduce exhaust temperature when necessary.

[0048] Pressure sensor 138 is located in pipe segment 142 downstream of pump 136 and upstream of branch pipe segment 144 to monitor the pressure output of pump 136. The sensed pressure can be used to confirm the output of pump 136 when the speed of pump 136 is set by control system 120, and can also be used to diagnose faults in pump 136 when the pressure reading does not match the expected level.

[0049] Multiple temperature sensors, including coolant temperature sensor 96, are included in engine system 20. Additionally, exhaust temperature sensor 150 is disposed adjacently upstream of tightly coupled catalytic converter 36, and exhaust temperature sensor 152 is disposed adjacently upstream of tightly coupled catalytic converter 38. Another exhaust temperature sensor 154 is disposed adjacently upstream of catalytic converter 40 between connector 44 and catalytic converter 40, and within pipe section 45. Another exhaust temperature sensor 156 is disposed adjacently upstream of mixer 56 and downstream of air injector 134 and catalytic converter 40, and within pipe section 47. Another exhaust temperature sensor 158 is disposed downstream of mixer 56 and within tailpipe 26. The locations of exhaust temperature sensors 150 and 152 are selected to measure the exhaust temperature exiting exhaust manifolds 32 and 34. The location of exhaust temperature sensor 154 is selected to measure the temperature of exhaust entering catalytic converter 40. The exhaust temperature sensor 156 is positioned to measure the temperature of the exhaust gas entering the mixer 56 and / or leaving the catalytic converter. The exhaust temperature sensor 158 is positioned to measure the temperature of the exhaust gas leaving the mixer 56.

[0050] An engine speed sensor 160 is disposed in or on the engine 22. For example, the engine speed sensor 160 can sense the crankshaft position, thereby providing input about the change in position from which the speed of the engine 22, particularly the angular velocity of the crankshaft, can be determined. In some embodiments, the engine speed sensor 160 can be configured to transmit a speed signal of the engine 22, such as in revolutions per minute.

[0051] Engine system 20, control system 120, exhaust system 24, and air injection system 130 handle various working fluids to achieve desired results. For example, with the air / fuel ratio delivered to the cylinders in a closed-loop control manner, the incoming air and fuel are processed by engine 22 using inputs from various sensors, including those in exhaust system 24, to correct for efficient operation and air / fuel consumption. Additionally, exhaust from engine 22 is efficiently processed by exhaust system 24, where reaction control is provided by air injection system 130. For example, two air injectors 132, 134 are positioned and operated to control the location where exothermic energy release occurs in exhaust system 24, where optimal reaction occurs over a favorable wide range of engine speeds and exhaust mass flow rates without exceeding component temperature limits.

[0052] refer to Figure 2The diagram schematically illustrates various aspects of the air injection system 130 and the control system 120. The air injection system 130 includes a pump 136, air injectors 132 and 134, check valves 146 and 148, pipe sections 140 and 142, and branch pipe sections 144 and 145. In this diagram, pipe section 142 is shown as including a buffer tank 170, which provides a sufficient amount of high-pressure air to ensure adequate supply to the air injectors 132 and 134, thereby meeting all operational requirements. A pressure sensor 138 is disposed in the buffer tank 170 to monitor the pressure therein. The pump 136 is operated to maintain the pressure in the buffer tank 170, and the check valve 172 suppresses backflow through pipe section 142 toward the pump 136. In addition to check valves 146 and 148 and air injectors 132 and 134, branch pipe sections 144 and 145 also include flow control valves 174 and 176 to control the flow rate supplied to air injectors 132 and 134. In some embodiments, air injectors 132 and 134 may themselves have controllable variable orifices, thus eliminating the need for separate flow control valves 174 and 176. In some embodiments, air may be supplied from another available source of engine 22, such as a turbocharger or supercharger, instead of including pump 136.

[0053] The control system 120 includes a controller 122, which may be an engine control module for engine 22. The controller 122 is coupled to mass flow controllers 178 and 180 to control each of flow control valves 174 and 176, respectively. The controller 122 is also coupled to an air pump controller 182 for controlling pump 136. The controller 122 is provided with data from a sensor group 184, which includes an engine speed sensor 160, oxygen sensors 124-127, and exhaust temperature sensors 154, 156, and 158. The mass flow controllers 178 and 180 may be full-function controllers configured similarly to the controller 122 described above. In other embodiments, the mass flow controllers 178 and 180 may have simplified functions for operation in conjunction with the controller 122.

[0054] Typically, the control system 120 and the air injection system 130 operate to draw air supply 186 into pump 136, pressurize the supplied air, and supply a precise amount of air as injected air 188 and injected air 190 to exhaust system 24 via air injectors 132 and 134. The total injected air can be one of injected air 188 and 190, both of them, or a combination of neither. In other words, depending on operating conditions, air may not be injected via air injectors 132 and 134, air may be injected via only one of air injectors 132 and 134, or air may be injected via both air injectors 132 and 134 at a separately determined mass rate.

[0055] The air injector 132, located upstream of the catalytic converter 40, can have a smaller injection orifice 162 compared to the larger injection orifice 164 of the air injector 134. In other words, the injection orifice 162 has a first openable flow area that is smaller in size than the second openable flow area of ​​the injection orifice 164. The smaller injection orifice 162 can be used for the upstream air injector 132 to improve mixing and provide more precise air injection. If needed, the larger injection orifice 164 can deliver a larger flow rate from the downstream air injector 134 to reduce exhaust temperature. The air injectors 132 and 134 can each operate within an airflow injection range, wherein the sizes of the injection orifices 162 and 164 are varied. By reducing the airflow injection range in which each air injector 132 and 134 operates, the air injection accuracy of both air injectors 132 and 134 can be improved.

[0056] refer to Figure 3 The illustration shows a portion of a control system 120 during operation of the air injection system 130, which is typically executed by mass flow controllers 178, 180 operated by controller 122, and is depicted as an air injection control system 300. For simplicity, the description may refer to a single controller, which means one or more controllers. The air injection control system 300 may be configured to include a CO and EQR calculation module 302, a reaction and air injection module 304, an air flow control module 306, and a data storage 308.

[0057] Combination Figure 3 Reference Figure 4 The diagram describes a process 400 for controlling the air injection system 130. Process 400 can operate continuously while the engine 22 is operating. In one embodiment, process 400 can operate only when stoichiometric operating conditions of the engine 22 are present. In other embodiments, process 400 can operate whenever excess CO or HC is present in the exhaust stream. Typically, the CO and EQR calculation module 302 calculates the current CO output and current EQR from the engine 22. In this embodiment, the CO and EQR calculation module 302 uses sensed data 310 including inputs from the mass airflow sensor 90, oxygen sensors 124-127, and engine speed sensor 160.

[0058] The calculation of 402CO can employ CO model data 312, such as that obtainable from data storage 308. The CO model can be constructed using physics-based methods, data-driven experimental methods, a combination thereof, or other means. For example, commercially available computational software can be used to create a CO model for high-fidelity simulations validated through target testing. In some embodiments, the CO model can be simplified and configured with predetermined values, such as using a lookup table where the CO level is tabulated by the oxygen content in the exhaust gas, to convert the sensed data 310 into a CO level. In some embodiments, 402CO can be calculated using only sensed data 310 from oxygen sensors 125, 127 downstream of the closely coupled catalytic converters 36, 38 to accurately determine exhaust conditions close to the catalytic converter 40.

[0059] The EQR calculation 404 uses EQR data 312, such as that obtainable from data storage 308, and exhaust oxygen data from oxygen sensors 124-127 in sensing data 310. As mentioned above, a fuel / air ratio can be used instead of the reverse air / fuel ratio. EQR calculation involves determining the current fuel / air ratio using sensing data 310 from oxygen sensors 124-127. The stoichiometric fuel / air ratio is typically obtainable from the engine control module of engine 22 and can be determined using air mass (such as from mass airflow sensor 90) and fuel mass entering engine 22 (such as from the fuel system, metered via injectors 106-113). The EQR is provided by comparing the current value with the stoichiometric value.

[0060] The reaction and air injection module 304 typically calculates the temperature rise of the exothermic reaction 406 and calculates a corrected airflow 408 to address the calculated temperature rise of the exothermic reaction 406. The calculated corrected airflow 408 is the airflow required for the injected air 188, 190, and is the opposite of the actual current airflow through the air injectors 132, 134.

[0061] Calculating the temperature rise of the exothermic reaction 406 includes calculating the temperature rise in the catalytic converter 406. The catalytic converter 40 contains a catalyst with a maximum temperature limit, which is ideally exposed to. For example, the maximum temperature limit could be 950 degrees Celsius. Additionally, the air injection rate of the air injection system 130 affects the amount of temperature rise in the catalytic converter 40. Therefore, information regarding the expected temperature rise in the catalytic converter 40 is useful in determining the level of air injection mass flow rate to be employed.

[0062] The reaction and air injection module 304 receives sensing data 316, which includes data from exhaust temperature sensors 154, 156, and 158, data from oxygen sensors 124-127, data from mass airflow sensor 90, and the current airflow mass rate through air injectors 132 and 134, such as from mass flow controllers 178 and 180. The reaction and air injection module 304 also obtains, for example, an exothermic model, an air injection model, and a CO rate from data storage 308.

[0063] The exothermic model can be a model of the exhaust system 24 and the air injection system 130, which can be used to determine the expected temperature rise in the catalytic converter 40 and optionally the mixer 56 (when included), based on available mathematics and currently sensed parameters, and the amount of air injected to consume the remaining CO and HC in the exhaust stream. The exothermic model can be constructed using physics-based methods, data-driven experimental methods, a combination thereof, or by other means. For example, the exothermic model can be created using commercially available computational software for high-fidelity simulations with target tests. In some embodiments, the exothermic model can be simplified and configured with predetermined values, such as in a lookup table, where sensed data values ​​are tabulated to convert sensed data 316 into the expected temperature rise.

[0064] The air injection model can be a model of exhaust system 24 and air injection system 130, which can be used to determine the preferred airflow rates through air injectors 132, 134 required to consume the remaining CO and HC in the exhaust stream based on available mathematics and currently sensed parameters. The airflow model can be constructed using physics-based methods, data-driven experimental methods, combinations thereof, or other means. For example, commercially available computational software can be used to create the airflow model for high-fidelity simulations with target tests. In some embodiments, the airflow model can be simplified and configured with predetermined values, such as in a lookup table, where sensed data values ​​are tabulated to convert sensed data 316 into preferred airflow values ​​undergoing a anticipated temperature rise (as described further below).

[0065] Calculating the exothermic reaction temperature rise (406) involves processing the sensed data (216) and CO rate using an exothermic model to obtain a value for the expected temperature rise in the catalytic converter (40) and mixer (56, if included). Calculating the corrected airflow (408) involves processing the sensed data (216), CO rate, and expected temperature rise using an airflow model to obtain the desired airflow through air injectors (132, 134).

[0066] Airflow control module 306 receives sensing data 324, CO rate, and corrected airflow. Sensing data 324 includes data from exhaust temperature sensors 154, 156, 158, mass airflow sensor 90, and engine speed sensor 160. Airflow control module 306 processes the data and transmits control signal 330 to air pump controller 182, control signal 332 to mass flow controller 178, and control signal 334 to mass flow controller 180. When coordinated among airflow control module 306, air pump controller 182, mass flow controller 178, and mass flow controller 180, the pump speed and the positions of flow control valves 174, 176 are set to supply the desired amount of air injected through air injectors 132, 134, thereby consuming residual CO, HC, and / or PM in the exhaust stream.

[0067] Under certain operating conditions, the reaction of exhaust components occurs only in the active catalyst within the catalytic converter 40, and not in sections approaching and exiting the converter 40, such as sections 42, 45, 46, and 47. The exothermic reaction within the catalytic converter 40 releases heat. Under certain operating conditions, the exothermic reaction required to consume all remaining CO and HC in the exhaust stream will raise the catalyst above its maximum temperature limit. Another complicating factor is that the exhaust temperature may not be high enough to cause a reaction to occur within the section itself. For example, when engine 22 operates at 4000 RPM or higher and in enriched conditions, the amount of CO and HC produced if consumed only in the catalytic converter 40 could cause a deviation exceeding the catalyst's maximum temperature limit. Furthermore, the amount of air injected through the air injector 132 is limited because excess air delivered to the catalytic converter 40 may raise the catalyst above its maximum temperature limit due to the increased rate of the exothermic reaction triggered by the added oxygen. In other words, injecting air only upstream of the catalytic converter 40 may be insufficient to completely consume the remaining CO and HC in the exhaust stream.

[0068] Therefore, the heat rise in the catalytic converter is managed by the airflow control module 306 to limit heat release in the catalytic converter 40. In this case, air can be injected before and after the air injectors 132 and 134, or only after the catalytic converter 40 via the air injector 134 when necessary. Under high load conditions of the engine 22, the combined method of injecting air into the exhaust system 24 via the air injectors 132 and / or 134 before and after the catalytic converter 40 ensures that the temperature of the catalyst in the catalytic converter 40 remains below its maximum temperature limit. Under such conditions, the exhaust temperature downstream of the catalytic converter 40 is high enough to complete the reaction in section 47 when air is injected via the air injector 134, and also in the mixer 56 (if included). Based on the sufficient temperature of the exhaust flow, the reaction in section 47 is initiated due to the air injection therein, even in the absence of an additional catalyst. Controller 122 controls the flow rates through air injectors 132 and 134, including injecting air to keep catalytic converter 40 below its maximum temperature limit while raising the temperature of the exhaust flow downstream of catalytic converter 40 in pipe section 47. Reactions in pipe sections before and / or after the catalytic converter enable the consumption of more CO and HC than could be consumed solely within catalytic converter 40, and allow the reaction location to be moved outside catalytic converter 40 to maintain the temperature below the catalyst's maximum temperature limit.

[0069] Using two air injection positions as described to control the location where the reaction and exothermic energy release occur allows for efficient conversion within a wider operating range of engine 22 (including ranges of engine speed, rich fuel emissions, and mass flow rates), while protecting components (e.g., catalysts) from their maximum temperature limits. Massive flow rates of CO and HC are converted via reaction by maximizing the exothermic oxidation capacity achievable within exhaust system 24 (including using only one primary catalytic converter 40 instead of adding a second dual-effect catalytic converter at additional cost).

[0070] The air injector 132 is positioned as far upstream of the catalytic converter 40 as possible, while still downstream of the tightly coupled catalytic converter 38. This allows for more reaction time in pipe sections 46, 45 and enables better mixing of the injected air with the exhaust gas, resulting in a more homogeneous mixture. In some embodiments, an optional mixer 149 may be included for further mixing. The mixer 149 may be, for example, a vortex mixer with internal blades or a spherical mixer. Better mixing also improves the reaction efficiency within the catalytic converter 40. Another advantage of initiating exothermic reactions in pipe sections 46, 45 is that the temperature of the exhaust gas traveling through them decreases due to the reaction, allowing more air to be injected without exceeding the maximum temperature limit of the catalyst in the catalytic converter 40.

[0071] In the example, when engine 22 operates to produce high-quality exhaust with high CO and HC content, but the exhaust temperature is not high enough to initiate a reaction in pipe section 47 downstream of catalytic converter 40, the distribution of air injection upstream of the catalytic converter via air injector 132 can be maximized to raise the temperature after neutralization in catalytic converter 40 to a high level sufficient for reaction (post-catalyst oxidation), including after air injector 134, solely based on sufficiently high exhaust temperatures without the presence of a catalyst. In embodiments where catalytic converter 40 is a dual-effect catalytic converter, the outlet temperature at exhaust temperature sensor 156 can be used to diagnose conversion performance by calculating the exothermic heat release during HC and CO conversion, which can then be used to correct the air injection quantity.

[0072] In embodiments where catalytic converter 40 is a three-way catalytic converter, the reactions of different contents are optimized. When a three-way catalytic converter is included, beneficial savings are achieved because in-tube conversion can be initiated, eliminating the need for a downstream two-way catalytic converter.

[0073] refer to Figure 5 Further details of the function of the airflow control module 306 are illustrated in process form as an injector balancing process 500, which can be executed within a submodule of the airflow control module 306. The injector balancing process 500 can begin 502 when the engine 22 is operating and can then run continuously until the engine 22 is shut down. In one embodiment, process 500 can operate only when stoichiometric operating conditions of the engine 22 are present. In other embodiments, process 500 can operate whenever excess CO or HC is present in the exhaust stream.

[0074] In process 500, it is determined whether 504EQR is greater than one. An EQR greater than 1.0 indicates that engine 22 is operating at a stoichiometric level. When 504 is determined to be positive and EQR is greater than one, it is determined whether 506 the exhaust temperature before catalytic converter 40 is below a first temperature threshold. For example, 506 could be a determination whether the reading of exhaust temperature sensor 154 is below 800 degrees Celsius. The first temperature threshold of 800 degrees Celsius is set at a level 150 degrees Celsius below the maximum temperature limit (950 degrees Celsius) of the catalyst in catalytic converter 40. When 506 is determined to be positive, meaning that the exhaust temperature before catalytic converter is less than the first temperature threshold, it is determined whether 508 the engine speed of engine 22 is below a speed threshold. For example, 508 could be a determination whether the reading of engine speed sensor 160 is less than 4000 RPM. When confirmed, this means that the speed of engine 22 is less than 4000 RPM. Processes 500 and 400 continue until air is injected 510 into exhaust system 24 only through air injector 132, and no air is injected through air injector 134. Through characteristic testing, a first temperature threshold was set 150 degrees Celsius below the maximum temperature limit of the catalyst, and an engine speed threshold was set at 4000 RPM. This characteristic testing has confirmed that below this threshold, CO and HC are completely converted using only air injected through air injector 132.

[0075] Returning to determination step 504, if EQR is not greater than one, no air injection is required, and determination 504 is repeated until the result is positive. When EQR is greater than one at determination 504 and the exhaust temperature before catalytic converter 40 is higher than a first temperature threshold at determination 506, process 500 continues to determination 514. Process 500 determines 514 whether the exhaust temperature before catalytic converter 40 is higher than a second temperature threshold. For example, determination 514 could be whether the reading of exhaust temperature sensor 154 is higher than 850 degrees Celsius. The second temperature threshold of 850 degrees Celsius is set at a level 100 degrees Celsius below the maximum temperature limit (950 degrees Celsius) of the catalyst in catalytic converter 40.

[0076] When 514 is determined to be negative, this means the exhaust temperature before the catalytic converter 40 is between 800°C and 850°C (the first temperature threshold and the second temperature threshold), and process 500 continues to inject 512 through air injectors 132 and 134. When 514 is determined to be positive, this means the exhaust temperature before the catalytic converter 40 is higher than the second temperature threshold (e.g., >850°C), and process 500 continues to determine 516 whether the engine speed 22 is higher than the speed threshold. For example, determination 516 could be whether the reading of engine speed sensor 160 is greater than 4000 RPM. When 516 is determined to be negative, this means the engine speed is not higher than the threshold (e.g., <4000 RPM), and process 500 continues to inject 512 through air injectors 132 and 134. When 516 is determined to be positive, this means the engine speed is higher than the threshold (e.g., >4000 RPM), and process 500 continues to inject 518 through air injector 134 only and not through air injector 132. As a result of the test, the second temperature threshold and engine speed threshold were set to 850°C and 4000 RPM, respectively. The test confirmed that only when air was injected through air injector 134 without air being injected through air injector 132, 99% of the CO and HC in the exhaust gas reacted and were converted.

[0077] When air 510 is injected via only one air injector 132, the feed rate at air injector 132 is fixed after the exhaust temperature sensor 156, located downstream of catalytic converter 40, reaches the catalyst's maximum temperature limit (e.g., 950°C), and air injection is initiated via air injector 134 in addition to air injector 132 to achieve the fully desired air injection feed rate. For operating conditions not covered above, both air injectors 132 and 134 are used to convert all CO and HC in the exhaust stream during stoichiometric operating conditions of engine 22 while keeping the catalyst below its maximum temperature limit (e.g., 950°C). It should be noted that under normal low-load operating conditions of engine 22, air injection into exhaust system 24 is generally not required. The exhaust temperature sensor 154 upstream of catalytic converter 40 helps control air injection via air injector 132. The exhaust temperature sensor 156 downstream of catalytic converter 40 helps determine CO and HC conversion levels and helps calculate heat release. Downstream of mixer 56, exhaust temperature sensor 158, such as EQR and exhaust flow rate, helps calculate the heat released during the conversion of CO and HC and calculate the air injection quantity.

[0078] Therefore, the engine system reduces tailpipe gaseous (hydrocarbons and / or carbon monoxide) and / or particulate emissions under a wide range of operating conditions, while not exceeding the maximum temperature limits of the components. Air is injected via one, two, or no air injectors. Two available air injectors are positioned with one before the under-plate catalytic converter and one after it.

[0079] In one embodiment, a temperature sensor preceding the bottom-plate catalytic converter is used to control upstream air injection, and a temperature sensor following the bottom-plate catalytic converter or downstream mixer can be used to diagnose conversion performance by calculating heat release during combustion. In another embodiment, a smaller injection orifice can be used for the upstream injector to improve mixing and deliver more precise air injection. If desired, a larger injection orifice / injection flow rate of the downstream air injector can be used to reduce exhaust temperature. When using a dual-effect catalytic converter, air injection through the upstream injector can be used to control catalyst temperature when the stoichiometric ratio is greater than 1.0, and can be used to achieve complete CO and HC reactions if desired.

[0080] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that numerous variations exist. It should also be understood that the one or more exemplary embodiments are merely examples and are not intended to limit the scope, applicability, or configuration of this disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient roadmap for implementing one or more exemplary embodiments. It should be understood that various changes can be made to the function and arrangement of the elements without departing from the scope of this disclosure as set forth in the appended claims and their legal equivalents.

Claims

1. An engine system, comprising: An engine is configured to consume fuel and air to produce exhaust flow. An exhaust system is configured to direct the exhaust flow from the engine to the tailpipe for discharge. The catalytic converter in the exhaust system; A first air injector is disposed in the exhaust system upstream of the catalytic converter and closer to the engine than the catalytic converter, and is configured to inject air into the exhaust system upstream of the catalytic converter; A second air injector is disposed in the exhaust system downstream of and adjacent to the catalytic converter, and is configured to inject air into the exhaust system downstream of the catalytic converter. as well as The controller is configured to: Air injection is achieved by controlling the flow rates through the first air injector and the second air injector only when the equivalence ratio of the engine is greater than one, including: When the temperature of the exhaust stream upstream of the catalytic converter is lower than the first threshold temperature, air is injected into the exhaust stream only through the first air injector; When the temperature of the exhaust stream upstream of the catalytic converter is higher than the second threshold temperature, air is injected into the exhaust stream solely through the second air injector; and When the temperature of the exhaust stream upstream of the catalytic converter is between the first threshold temperature and the second threshold temperature, air is injected into the exhaust stream by both the first air injector and the second air injector, wherein the first threshold temperature is less than the second threshold temperature.

2. The engine system according to claim 1, comprising: A first temperature sensor is located in the exhaust system upstream of the catalytic converter; A second temperature sensor is located in the exhaust system downstream of the catalytic converter; as well as At least one controller is configured to control the flow rates through the first air injector and the second air injector. The at least one controller is configured to control the flow rate through the first air injector based on the first temperature sensor. The at least one controller is configured to diagnose the conversion performance of the catalytic converter by calculating the released heat based on the second temperature sensor.

3. The engine system of claim 1, wherein the first air injector includes a first orifice having a first flow area, and the second air injector includes a second flow area, and the engine system includes a controller configured to control the flow rates through the first air injector and the second air injector, including injecting air through at least one of the first air injector and the second air injector to keep the catalytic converter below a maximum temperature limit, wherein the first flow area is smaller than the second flow area to improve the mixing and precision of the flow rates through the first air injector and to optimize the exhaust temperature reduction caused by the flow rates through the second air injector.

4. The engine system of claim 1, further comprising a controller configured to control air injection through the first air injector and the second air injector based on an equivalence ratio of the engine during operation, wherein the equivalence ratio represents the fuel-air ratio of the engine during operation compared with the stoichiometric ratio of the engine, wherein when the catalytic converter comprises a dual-effect catalytic converter and the equivalence ratio is greater than one, the controller is configured to control the temperature in the catalytic converter to achieve a complete carbon monoxide and hydrocarbon reaction.

5. A method comprising: To configure an engine system to consume fuel and air to produce exhaust flow; The exhaust flow is directed from the engine to the tailpipe via the exhaust system for discharge; A catalytic converter is installed in the exhaust system; Air is injected into the exhaust system upstream of the catalytic converter via a first air injector located in the exhaust system upstream of the catalytic converter, for a first set of operating conditions of the engine. as well as Air is injected into the exhaust system downstream of the catalytic converter via a second air injector located downstream of the catalytic converter, for a second set of engine operating conditions. The method further includes: controlling the flow rates through the first air injector and the second air injector via a controller to achieve air injection only when the equivalence ratio of the engine is greater than one, which includes: Air is injected into the exhaust stream solely through the first air injector when the temperature of the exhaust stream upstream of the catalytic converter is below a first threshold temperature, via the controller. Air is injected into the exhaust stream solely through the second air injector when the temperature of the exhaust stream upstream of the catalytic converter is higher than a second threshold temperature, via the controller. Air is injected into the exhaust stream by both the first and second air injectors via the controller when the temperature of the exhaust stream upstream of the catalytic converter is between the first threshold temperature and the second threshold temperature, wherein the first threshold temperature is less than the second threshold temperature.

6. The method of claim 5, further comprising controlling the flow rates through the first air injector and the second air injector via a controller; and injecting air through at least one of the first air injector and the second air injector to keep the catalytic converter below a maximum temperature limit while increasing the temperature of the exhaust stream downstream of the catalytic converter.

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